1. Field of the Invention
This invention relates to toilet waste tanks for vehicles, and in particular to systems in which human waste materials are chemically treated and stored in a relatively small tank which will periodically be emptied into a sewage system. In accordance with the modern trend to protection of the environment, such systems are especially designed to prevent the escape of untreated liquid or solid wastes, and also to limit the escape of noxious odors. Effective, simple servicing procedures are necessary so that rest rooms stay sanitary and clean-smelling.
2. Description of the Prior Art
Prior art sanitary waste tanks for vehicles fall into a number of categories, ranging from the very simple to the fairly complicated. U.S. Pat. No. 2,094,537 shows an early chemical toilet apparatus in which provision is made to prevent the escape of contents during motion of the vehicle or when the toilet is not in use. When the toilet seat is lowered, a large valve directly below the seat completely closes off the main opening into the storage tank, so that neither liquid nor gasses can escape to the interior of the vehicle. A simple ventilation pipe connects from the top surface of the tank, typically up through the roof of the vehicle. This type of installation suffers the disadvantage that unpleasant odors may rise into the vehicle when the seat is opened, because there is no provision to ensure that in the open seat condition air flow will be down through the toilet opening into the interior of the tank and up the vent pipe.
U.S. Pat. No. 3,583,675 is concerned with a recirculating toilet system for a vehicle, in which a chemically treated liquid is pumped from the bottom of a tank to flow along exposed surfaces of a toilet bowl and to remove contents clinging to those surfaces down to the tank. If such a recirculating toilet is used so often that the liquid becomes heavily contaminated, then each time the tank is flushed this contaminated water flows along an exposed surface from which odors can be released to the interior of the vehicle. Toilets of this general type are not equipped with a positive ventilation system that removes odors rising from the liquid surface by way of a vent pipe such that they will be released in a place which is not offensive to the vehicle occupants. Further, known designs of recirculating toilets of this general type render thorough interior cleaning very difficult, because there is no access to the interior of the holding tank except through the relatively small opening through which wastes pass from the toilet bowl, or by disassembly and removal of the entire pump unit. Further, when these units are serviced by relatively unskilled personnel, problems sometimes arise because the wrong amount of fresh water is added to the tank. In particular, if too much fresh water is added this time, the effectiveness of the chemicals is reduced, and the usage capacity of the toilet before it becomes overfull is also reduced.